Lateral Earth Pressure and Displacement of Geosynthetic Reinforced Soil (GRS) Walls

1. Lateral Earth Pressure and Displacement of Geosynthetic Reinforced Soil (GRS) Walls Thang Pham, PhD Dept. of Civil Engineering UTRGV Nov. 16, 2017

2. Outline • Introduction of the GRS Application • Literature Review of Design Methods for GRS Walls • Behavior of GRS Composite • Model for Lateral Stress and Displacement of a GRS Wall • Finite Element Analysis • Conclusions

3. GRS wall: GRS mass facing element GRS mass: compacted soil geosynthetic reinforcement Facing element: many types  modular block facing is the most common Introduction a GRS wall with modular block facing

4. GRS wall: GRS mass facing element Introduction a GRS wall with reinforced concrete facing

5. Block-Faced GRS WallDeBeque Canyon, CO

6. Block-FacedGRS Wall(France)

7. Rock-Faced GRS Bridge Abutment Black Hawk, CO

8. Block-Faced GRS Bridge Abutment Defiance County, OH

9. Rock-Faced GRS wallBloomfield, CO

10. Block-Faced Rockfall Barrier GRS Wall Wolf Creek Pass, CO

11. Block-Faced GRS Wall, Grand County, CO

12. Behavior of GRS Composite

13. Current Design Methods for GRS Walls • Prevailing design methods for GRS walls: • AASHTO method (2002) • NCMA method (Collin, 2002) • NHI method (Elias, et al., 2001) • based on design of “conventional” retaining walls with the addition of reinforcement acting as “tiebacks”

14. “Tieback” design concept: From Experiments  Sv plays a much greater role than Tf.

15. Full-scale experiments (Adams, 1997; Adams, et al., 2007 )  Sv plays a much greater role than Tf.

16. Behavior of a GRS mass (continued) Unconfined Compression Test on “Mini Pier” (Adams, 1997 )

17. Behavior of a GRS mass (continued) Unconfined Compression Test (Elton and Patawaran, 2005 )

18. Full-scale experiments (Pham, 2009) Finishing Preparation of Specimen

19. Full-scale experiments (Pham, 2009)

20. Test 2: Lateral Displacement

21. FE Analysis: Steps of Analysis

22. FE Analysis for Test 2: Stress-Strain Curve

23. FE Analysis for Test 2: Lateral Displacement

24. FE Analysis for Test 2: Internal Movement

25. FE Analysis for Test 2: Reinforcement Strain

26. Behavior of GRS Composite

27. Reinforcing Mechanisms • Concept of enhanced apparent cohesion(Scholosser and Long, 1972; Ingold, 1982) • Concept of increase of apparent confining pressure (Yang and Singh, 1974; Hausmann, 1976; Ingold, 1982, Athanasopoulos, 1994,) • Concept of reduced angle of dilation (Pham, 2009)

28. Reinforcing Mechanisms Concept of Apparent Cohesion Concept of Apparent Confining Pressure

29. The Model is developed Based on: • Schlosser and Long (1972): Concept of Apparent Cohesion • Ketchart and Wu (2001): Concept of Average Stress Analytical Model Strength Properties of a GRS Composite

30. Schlosser and Long (1972) Analytical Model Strength Properties of a GRS Composite Concept of Apparent Confining Pressure and Apparent Cohesion

31. FHWA-HRT-10-077 Proposed Model for Strength Properties of a GRS Composite GRS Integrated Bridge System Interim Implementation Guide (FHWA-HRT-11-206).

32. Model for Lateral Earth Stress and Lateral Displacement of a GRS Wall

33. Lateral Earth Stress of a GRS Wall • Due to the constraints to lateral deformation of a reinforced soil mass (resulting from frictional resistance at the soil-reinforcement interface), the lateral earth pressure against the wall face has been found much smaller than the lateral stress within a reinforced soil mass. • Field measured data have indicated that the lateral earth pressure varies little with depth in closely spaced reinforced soil walls; and that the AASHTO’s active earth pressure equation Eqn. (1) hardly applies.

34. Lateral Earth Stress of a GRS Wall • The lateral stress in the soil elements situated against the facing of a GRS wall, as obtained from FE analysis, is not equal to the lateral earth pressure. • The lateral earth pressure can however be deduced by distributing the load in the reinforcement layer adjacent to the facing over the tributary area of the facing based on equilibrium of forces.

35. A typical GRS wall with a modular block facing

36. Exiting Methods for Estimating Lateral Movement • FHWA Method (Christopher, et al., 1989) • Geoservices Method (Giroud, 1989) • CTI Method (Wu, 1994) • Jewell-Milligan Method (1989) (All ignored facing Stiffness)

37. h of the wall face at depth zi : Lateral Movement of GRS Walls (Cont.) (equation a) Prm = Reinforcement force at zone 1

38. Lateral Stress, Displacement and Connection Forces for GRS walls with Modular Block Facing • Assumptions: • The wall face is vertical or near vertical. • A uniform vertical surcharge is applied over the entire horizontal crest of the wall. • Each facing block is a rigid body: movement is allowed, but no deformation of the blocks.

39. Connection Forces of GRS Walls (cont.) A typical GRS wall with a modular block facing

40. Connection Forces of GRS Walls (cont.) (equation b)

41. Lateral Earth Pressure of a GRS Wall with modular block facing

42. Lateral Erath Pressure of a GRS Wall with modular block facing

43. Estimating Lateral Movement of GRS Walls with Modular Block Facing • Movement of a GRS wall with modular block facing at depth zi can be determined as (substituting equ. (b) into (a)): • If the friction between the back of the wall face and the soil is ignored, the wall movement at depth zi can be determined as:

44. Lateral displacements of Jewell-Milligan method and the proposed method (with b = 0 kN/m3) Comparisons with Jewell-Milligan Method (1989)

45. Lateral displacements of Jewell-Milligan method and the proposed method (with b = 20 kN/m3) Comparisons with Jewell-Milligan Method (1989)(cont.)

46. Configuration of the Wall (Hatami and Bathurst 2005, 2006)

47. Compare the Analytical Modelwith Full-Scale Test Results by Hatami and Bathurst (2005 & 2006) (cont.)

48. Concluding Remarks • The lateral earth pressure against the wall face has been found much smaller than the lateral stress within a reinforced soil mass. • The analytical Model is capable of determining wall deflection as affected by the rigidity of wall facing, and overcomes a major shortcoming of the current method. • The Model can also be used to determine the connection forces at the wall face.

49. Thank you !